Arc Circle Syntax

I cannot find any information on what the tex command is to create the arc symbol over letters like the following image: http://www.mathwarehouse.com/images/questions/arc/arc-CH_CCCCFF.jpg

Does anyone know the tex for this (which I hope MathJax supports ;)

---

If you add

<script type="text/x-mathjax-config">
  MathJax.Hub.Config({
    TeX: { Augment: {
      Definitions: {
        macros: {
          overparen: ['UnderOver','23DC'],
          underparen: ['UnderOver','23DD']
        }
      }
    }}
  });
</script>

before the script that loads MathJax.js, then you can use

$\overparen{\rm CH}$

to get a paren over the CH. Alternatively, you can use

\overset{\mmlToken{mo}{⏜}}{XYZ}

to get a similar effect. The STIX fonts include several sizes of the overparen (though the bounding box data in the font isn't correct, so one size is placed a bit too low), but with the MathJax web fonts, they will be flat in the center most of the time.

This is not exactly what you have, but it is close.